Don't process the prompt line

The Write Commands Until Expected Prompt Keyword
executes a command and then reads output until it sees
the prompt. It then returns all that read output. This
output is then split into lines - which means you get
the prompt line also.

This patch instructs Split To Lines to ignore the last
line (-1).

Change-Id: Ifea842f5b0fa0c45818be4e9cbaa2f0b33774af6
Signed-off-by: Sam Hague <shague@redhat.com>